Thin film deposition is a vital aspect of semiconductor manufacture. In order to produce an integrated circuit, thin films of various materials are used as barriers to the diffusion or implantation of impurity atoms, or as insulators between conductive materials and the silicon substrate. Typically, holes or windows are cut through the barrier material wherever impurity penetration or contact is required.
A mask is used to form the necessary pattern or windows or holes on the surface of the silicon substrate. The patterns are first transferred from the mask to a light-sensitive photoresist. Chemical or plasma etching is then used to transfer the pattern from the photoresist to the barrier material on the surface of the silicon substrate. Each mask step requires successful completion of numerous processing steps.
Ion implantation is commonly used in manufacturing semiconductors to introduce impurity atoms into the silicon substrate, and offers certain advantages over high temperature diffusion. Generally, an ion implanter is a high-voltage particle accelerator producing a high-velocity beam of impurity ions which can penetrate the surface of silicon target wafers. The ion-source operates at a high voltage of, for example, 25 kV, and produces a plasma containing the desired impurity as well as other undesired species. An accelerator column adds energy to the beam, for example, up to 175 keV, and accelerates the ions to their final velocity.
In semiconductor manufacturing, as well as other processing fields, there is a continuing need for improved selected area deposition techniques. In many applications it is desirable to be able to deposit material on a selective basis so as to build up films in certain complex patterned regions of a substrate, but not in other adjacent regions. An example in the semiconductor art is the filling of via holes and trenches with conducting metallic films during integrated circuit manufacturing.
Ion deposition of thin films has been described in "Film Deposition and Buried Layer Formation By Mass-Analyzed Ion Beams" by I. Yamada et al. in Nuclear Instruments and Methods in Physics Research B6, 439-446 (1985 North-Holland, Amsterdam). In this publication, Si was metallized by a mass-analyzed ion beam to form Pb thin films.
Ion deposition has been described in the following U.S. patents:
U.S. Pat. No. 4,480,010 to Sasanuma et al. describes a method and apparatus for coating materials by ion plating. A negative potential relative to that of the vapor source is applied to the substrate in order to facilitate the bombardment effect. At the intermediate stage of the process, the potential of the substrate is left floating while the ionization means is being driven in order to control the bombardment effect.
U.S. Pat. No. 4,155,735 to Ernsberger describes an electromigration method for making stained glass photomasks. Stain-producing ions are migrated into the surface of the glass under the influence of an electric field and moderately elevated temperatures. Positive potential is applied to two electrode layers to cause the migration of mobile cations out of specific zones of the glass underlying a photoresist.
U.S. Pat. No. 4,944,961 to Lu et al. describes the deposition of metals on stepped surfaces using an ionized beam technique. Ionized vapor is drawn to a substrate by an imposed bias.
U.S. Pat. No. 5,128,173 to Kugan describes a process for deposition of inorganic materials using an ionized beam technique. A deposition area is negatively charged to attract positively charged ions from the deposition material.
Japanese patent 53-18183 describes a process for selectively depositing an ionized substance onto a desired area of an electrically conductive substrate in which the rest of the substrate is first covered with an insulating film.
A continuing need exists for improved apparatuses and methods for selective area deposition of thin films onto substrates.